1. Field of the Invention
The present invention relates to a wrist structure unit provided at a tip of an arm of an industrial robot.
2. Description of the Related Art
A wrist structure unit of an industrial robot includes a wrist machine frame and a wrist inner frame rotatable relative to the wrist machine frame. Various wrist elements, such as a hand and a tool, are attached to the wrist inner frame via a working tool attachment member. Rotation of an output shaft of a driving motor incorporated in the wrist machine frame is decelerated by a spur gear deceleration mechanism unit, thereby rotating the wrist inner frame relative to the wrist machine frame.
Japanese Laid-open Patent Publication No. 2014-000612 has disclosed a wrist structure unit that includes a decelerator chamber housing a spur gear deceleration mechanism unit that stores a driving motor in a wrist machine frame to form a driving force transmission mechanism and a wiring chamber housing wiring cables for supplying a driving power to the driving motor and transmitting and receiving control signals, in which the chambers are formed to be apart from each other. Accordingly, maintenance of the driving motor can be performed independently at the wiring chamber side via the wiring cables, thus ensuring easy maintenance.
Additionally, in the above Patent Publication, only a spur gear transmission mechanism allows deceleration and transmission by one wrist operation system of a wrist having a plurality of degrees of operational freedom. This structure can exclude a complicated deceleration mechanism in which a belt-pulley mechanism coexists, resulting in the reduction of production cost.
In the Patent Publication, the spur gear deceleration mechanism that consists of a three-stage spur gear train is arranged on one side of the wrist machine frame. A single-stage spur gear has a deceleration ratio ranging from 1:2.5 to 1:7 (about 4), so that the three-stage spur gear train can achieve a deceleration ratio of from 40 to 80. In addition, Japanese Laid-open Patent Publication No. H07-052074 discloses a spur gear deceleration mechanism. Furthermore, in Japanese Laid-open Patent Publication No. H10-175188, a fifth axis deceleration mechanism is also a spur gear deceleration mechanism whose driving motor is arranged in a wrist chamber.
However, in the spur gear deceleration mechanisms of Japanese Laid-open Patent Publication Nos. 2014-000612 and H07-052074 and the fifth axis deceleration mechanism of Japanese Laid-open Patent Publication No. 10-175188, when deceleration ratio needs to be changed due to a change in specifications, such as an increase in portable mass, design changes such as the preparation of a new wrist machine frame are needed.
The present invention has been accomplished in view of such circumstances. It is an object of the present invention to provide a wrist structure unit that can easily change deceleration ratio without newly forming a wrist machine frame.